Apparatus for polishing thin, flat semi-conductor wafers is well-known in the art. Such apparatus normally includes a polishing head which carries a membrane for engaging and forcing a semi-conductor wafer against a wetted polishing surface, such as a polishing pad. Either the pad, or the polishing head is rotated and oscillates the wafer over the polishing surface. The polishing head is forced downwardly onto the polishing surface by a pressurized air system or, similar arrangement. The downward force pressing the polishing head against the polishing surface can be adjusted as desired. The polishing head is typically mounted on an elongated pivoting carrier arm, which can move the pressure head between several operative positions. In one operative position, the carrier arm positions a wafer mounted on the pressure head in contact with the polishing pad. In order to remove the wafer from contact with the polishing surface, the carrier arm is first pivoted upwardly to lift the pressure head and wafer from the polishing surface. The carrier arm is then pivoted laterally to move the pressure head and wafer carried by the pressure head to an auxiliary wafer processing station. The auxiliary processing station may include, for example, a station for cleaning the wafer and/or polishing head; a wafer unload station; or, a wafer load station.
More recently, chemical-mechanical polishing (CMP) apparatus has been employed in combination with a pneumatically actuated polishing head. CMP apparatus is used primarily for polishing the front face or device side of a semi-conductor wafer during the fabrication of semiconductor devices on the wafer. A wafer is "planarized" or smoothed one or more times during a fabrication process in order for the top surface of the wafer to be as flat as possible. A wafer is polished by being placed on a carrier and pressed face down onto a polishing pad covered with a slurry of colloidal silica or alumina in de-ionized water.
A schematic of a typical CMP apparatus is shown in FIGS. 1A and 1B. The apparatus 10 for chemical mechanical polishing consists of a rotating wafer holder 14 that holds the wafer 10, the appropriate slurry 24, and a polishing pad 12 which is normally mounted to a rotating table 26 by adhesive means. The polishing pad 12 is applied to the wafer surface 22 at a specific pressure. The chemical mechanical polishing method can be used to provide a planar surface on dielectric layers, on deep and shallow trenches that are filled with polysilicon or oxide, and on various metal films. CMP polishing results from a combination of chemical and mechanical effects. A possible mechanism for the CMP process involves the formation of a chemically altered layer at the surface of the material being polished. The layer is mechanically removed from the underlying bulk material. An altered layer is then regrown on the surface while the process is repeated again. For instance, in metal polishing a metal oxide may be formed and removed repeatedly.
A polishing pad is typically constructed in two layers overlying a platen with the resilient layer as the outer layer of the pad. The layers are typically made of polyurethane and may include a filler for controlling the dimensional stability of the layers. The polishing pad is usually several times the diameter of a wafer and the wafer is kept off-center on the pad to prevent polishing a non-planar surface onto the wafer. The wafer is also rotated to prevent polishing a taper into the wafer. Although the axis of rotation of the wafer and the axis of rotation of the pad are not collinear, the axes must be parallel. Polishing heads of the type described above used in the CMP process are shown in U.S. Pat. No. 4,141,180 to Gill, Jr., et al.; U.S. Pat. No. 5,205,082 to Shendon et al; and, U.S. Pat. No. 5,643,061 to Jackson, et al. It is known in the art that uniformity in wafer polishing is a function of pressure, velocity and the concentration of chemicals. Edge exclusion is caused, in part, by non-uniform pressure on a wafer. The problem is reduced somewhat through the use of a retaining ring which engages the polishing pad, as shown in the Shendon et al patent.
Referring now to FIG. 1C, wherein an improved CMP head, sometimes referred to as a Titan head which differs from conventional CMP heads in two major respects is shown. First, the Titan head employs a compliant wafer carrier and second, it utilizes a mechanical linkage (not shown) to constrain tilting of the head, thereby maintaining planarity relative to a polishing pad 12, which in turn allows the head to achieve more uniform flatness of the wafer during polishing. The wafer 10 has one entire face thereof engaged by a flexible membrane 16, which biases the opposite face of the wafer 10 into face-to-face engagement with the polishing pad 12. The polishing head and/or pad 12 are moved relative to each other, in a motion to effect polishing of the wafer 10. The polishing head includes an outer retaining ring 14 surrounding the membrane 16, which also engages the polishing pad 12 and functions to hold the head in a steady, desired position during the polishing process. As shown in Figure IC, both the retaining ring 14 and the membrane 16 are urged downwardly toward the polishing pad 12 by a linear force indicated by the numeral 18 which is effected through a pneumatic system.
The polishing pad 12 is a consumable item used in a semiconductor wafer fabrication process. For instance, under normal wafer fab conditions, the polishing pad must be replaced aft er a usage of between 12 and 18 hours. The removal of a polishing pad from a table is therefore an important task in the operation of a CMP process. Since the pad is normally mounted to the rotating table by adhesive means, the removal of the polishing pad for replacement presents great difficulties. Conventionally, to remove a polishing pad from a table, a pair of pliers is first used to pry loose the edge of the pad from the table. The edge of the pad is then clamped by the pair of pliers and pulled manually by a machine operator. Since the adhesive bond is very strong, manual removal by using a pair of pliers is cumbersome and frequently causes personal injury to a machine operator when the pliers slips from the polishing pad.
It is therefore an object of the present invention to provide a method for removing an adhesive bonded pad from a backing plate that does not have the drawbacks or shortcomings of the conventional methods.
It is another object of the present invention to provide a method for removing an adhesive bonded pad from a backing plate that can be practiced without causing safety problems to a machine operator.
It is a further object of the present invention to provide a method for removing an adhesive bonded pad from a backing plate by utilizing a specially designed tool of a T-shaped removal bar.
It is another further object of the present invention to provide a method for removing an adhesive bonded pad from a backing plate by utilizing a T-shaped removal bar which has a tip equipped with fastening means for fastening to the pad.
It is stiff another object of the present invention to provide a method for removing an adhesive bonded pad from a backing plate by using a T-shaped removal bar in a rotational motion of the bar to break the adhesive bond between the pad and a table to which the pad is bonded.
It is yet another object of the present invention to provide a method for removing an adhesive bonded pad from a backing plate by utilizing a T-shaped removal bar and shear force to remove the pad.
It is still another further object of the present invention to provide an apparatus for removing an adhesive bonded pad from a backing plate which is constructed in a T-shaped bar equipped with a fastening device at the tip of the T for fastening to a pad.
It is yet another further object of the present invention to provide an apparatus for removing an adhesive bonded pad from a backing plate which is constructed of a circular cross-sectional tubing for easier rotation and removal of the pad by shear force.